Afterburners are systems that provide a temporary increase in jet engine thrust. They work by injecting into the engine nozzle region downstream of the combustion chamber additional fuel, which ignites due to the presence of unused oxygen in the exhaust stream. The ignited fuel produces a blowtorch effect, increasing the temperature and velocity of the exhaust gas shooting through the nozzle, which increases thrust.
Because of the inefficiencies inherent in most afterburner systems, primarily in the form of extra fuel consumption, afterburners typically are used in limited conditions, such as during take offs, when entering supersonic speeds, and during military combat maneuvers where a burst of speed is beneficial. (Afterburners can provide a short increase in thrust in military aircraft of between 40 and 70 percent.)
The jet engine nozzles used with afterburner systems must be able to open wider to accommodate the reduced density of exhaust gas. These special configuration nozzles, aka variable area nozzles, can be found in both military (fighter) jets and commercial (supersonic and business) jets equipped with afterburners.
Exhaust gas exiting the afterburners of high velocity jet engines can create undesirably high levels of noise, particularly mixing noise and shock noise. Mixing noise is a result of the mixing of the jet exhaust gas with the surrounding ambient air (and caused by the difference in shear), and generally increases as nozzle exhaust gas velocity increases. Shock noise is caused by shock waves generated in the engine exhaust plume of jets operating at supersonic speeds.
Thus there is a need for a system and method to reduce the high noise levels caused by jet engines equipped with afterburners.